Method for drying fibrous sheet material



April 1, 1952 J. DUNGLER METHOD FOR DRYING FIBROUS SHEET MATERIAL FiledDec. 21, 1948 2 SHEETS-SHEET 1 i M a 1 ,m W M. 7/ Q Q QM 35% /\N A ril1, 1952 J. DU NGLER METHOD FOR DRYING FIBROUS SHEET MATERIAL Filed Dec.'21, 1948 2 SHEETSSHEET 2 LI I IL l l l nMH .llll'l R q u Patented Apr.1, 1952 METHOD FOR DRYING FIBROUS SHEET MATERIAL J ulicn Dungler, Basel,Switzerland Application December 21, 1948, Serial No. 66,519 In FranceDecember 31, 1947 1 Claim. 1

The present invention relates to a method of and an apparatus for dryingfabrics, paper and similar fibrous sheet material.

The method ordinarily used for drying fabrics, which have undergone, forexample, a dyeing or finishing or similar treatment, consists in blowinghot air upon the fabric or fiber material while it travels in acontinuous motion past a blowing device. The temperature of the heatedair vary according to the nature of the drier apparatus and are mostlykept below 100 C. The moisture-laden air is continuously removed by aventilating system and is replaced by a corresponding quantity offreshair. These apparatus generally operate on the principle of counterfiow, whereby the intake of fresh air occurs at the discharge end of theapparatus in such manner that the material to be treated prior toleaving the machine, comes into contact with hot and dry air. Such aprocess is rather uneconomical, even if the drying is effected in aheat-insulated chamber, in view of the fact that the moisture-laden butstill hot air must be constantly removed, thus resulting in appreciablelosses of heat. Another inconvenience of this process resides in theoverdrying of the treated material which, in the case of a fabric,renders it hard and brittle, on the one hand, and results in a loss oftime and heat on account of the unnecessary expulsion of moisture on theother hand.

The present invention concerns a drying processwhich avoids these andother disadvantages and has as one of its objects to provide meansensuringa predetermined moisture content in the treated material.

A further object of the invention is to provide means affording thesteps of effectively vaporizing and drying the fabric or other materialwithin the inner fiber layers thereof as well as on its surface, wherebythe time for eliminating or driving out excessiy e moisture may beappreciably cut.

Another objector the present invention is to provide means permittingtreatment of elongated material, such as a roll of fabric, in a veryeconomical and uniform manner from start to finish to thereby obtain apredetermined degree of dryness.

A further object of this invention is to provide means for exposing thematerial to be dried to a gaseous atmosphere of elevated temperature;moisture, temperature and time of exposure bein related and controlledsoas to result in a predetermined or desired degree of dryness of thematerial.

A still further object of the invention is to provide means capableofmaintaining humidity and pressure of the atmosphere within-'afheatingor treatment chamber at predetermined levels.

Yet a further object of the'inven'tion' is to provide meansfacilitatingpassage of fabric .tobe treated in a continuous path throughatreatment chamber, whose inlet and outlet aree'ffectively preventedfrom losing any appreciable amount of heat from within said chamberwhile the fabric or material is conveyed to and from said chamber.

It is also an object of the present invention to provide meansutilizingand/or reutilizing ina very efiicaciousmanner at least part'ofthe moisture driven out of the materialunder treatment.

More specifically, it is an object ofthis invention to provide meansrendering the possibility of withdrawing or extracting moisture fromthematerial under treatment by exposing said material to superheated steam,vapor or similar fluid.

A further object of the invention-is toiprovide means contributing tothe conversion of moisture driven out of the material into superheatedsteam or vapor which is adapted to extract further moisture from saidmaterial.

The above and other'objects of the invention will become more apparentfrom the following description of preferred embodiments, reference beinghad to the accompanying drawings in which:

Fig. 1 shows, schematically, a longitudinalsection of an apparatusaccording to the invention.

Fig. 2 is an end elevation of the apparatus of Fig. 1; and

Fig. 3 isa sectional view similar to-tthat of Fig. 1, showing a modifiedform of an apparatus according to the invention.

Referring now more particularly "to Figs. 1 and 2, there is shown aheat-insulated chamber I provided with two rectangular slots "2 and '3"in the opposite walls 2a, 2b thereof, these slots forming the deliveryand discharge end, respectivelyj for fibrous sheet material or similararticle 5 such as a piece of fabric, which'is'tobetreated and which issupplied in bulk and in continuous fashion by means of feed rollers 5 toand'removed from said chamber by means of engageable V rollers 6.

Within the chamber l there are "providedtwo flexible and porous conveyormeans I and 38 passing over rollers 9 and [0, respectively; theseconveyor means may consist of endless wideime'sh wire bands,spaced-apart and-guided perforated belts of nylon, sisal, hemp and thelike or endless and contiguous chains, and are designed to guide thefabric 4 during its passage through said chamber I while the surface ofthe fabric remains accessible to the drying fluid.

The continuous and uniform drive of these conveyor means I, is indicatedin dotted lines in Fig. 1 for claritys sake.

Two blower units II and I2 are disposed in the upper and lower half,respectively, of chamber I. These units are provided, at their sidesfacing the fabric 4, with respective sets of discharge tubes or nozzlesI3 and I4 of any suitable construction such as described in my copendingU. S. application Serial No. 762,776, filed July 2 2, 1947, now PatentNo. 2,495,163. Furthermore, the blower units II and I2 are equipped withblowers I5 and I6, respectively, whose respective intake pipes I? and I8open into the interior of chamber I.

A pair of preferably electric-operated heating elements,schematicallyindicated at 20 and 2|, are mounted in the blower units II and I2,respectively, for heating the drying fluid which the blowers I5 and I6discharge through upper and lower nozzles I3 and I4.

Two pairs of slidable plates 22 and 23 are arranged above and below thefeed or entrance slot 2 and, the exit or discharge slot 3, respectively,in such fashion as to be capable of at least partially blocking orcovering these slots in an adjustable manner. Plates 22 and 23 may befixed in their positions by means of wing nuts 24 engaging threadedbolts 25 which are mounted on the end walls 2a, 2b of chamber I and passthrough elongated guide holes 25 provided in said plates 22 and 23.

The operation of the above-described apparatus is as follows:

At the beginningof the drying or treatment operation, the chamber I isfilled with air which is drawn into the pipes I! and It by the blowersI5 and I6, respectively, and is forced out through the nozzles I3, l4after having been heated by the heating elements 20, 2|. The air leavingthe discharge nozzles I3, I4 impinges upon the surface of the fabric orother article & passing intermediate said sets of nozzles.

According to an important feature of the invention, the heating elements23 and 2i raise the gaseous fluid leaving the nozzles I3, I4 to atemperature higher than the boiling point of the liquid which permeatesand is contained in fabric 4.

In the case where the liquid to be expelled is water, the temperature ofthe discharged gaseous fluid is preferably raised to a value between 110and 130 C., or even higher, if the article under treatment is capable ofwithstanding such higher temperature.

Assuming the most common case of the liquid to be expelled being water,the air initially present in the chamber I is thus raised toapproximately 120 C'. The contact of this hot air with the fabric 4causes the evaporation of the water contained within the fabric fibers.Since theair temperature is above 100 C., the water already evaporatedwill be unable to condense, so that the chamber I will become more andmore filled with continuously produced water vapor by the action of thedrying fluid which is discharged through the tubes or nozzles I3, I4upon the fabric i. Asa -result, the pressure mountsinside the chamber,thereby giving rise to aflo'w of'the gaseous fluid which tends to escapethrough slots 2, 3 so as to equalize the pressure prevailing inside thechamber with that of the atmosphere.

According to another feature of the invention,

the intake pipes IT, IS of the blowers I5, I5 feed the nozzles I3, I4,which discharge into the interior of the chamber I, by drawing upon thegaseous fluid existing within the chamber. Since vapor is continuouslyproduced inside the chamber and, for the major part, is recirculated bythe blowers I5, I6 upon the continuously moving fabric 4 after beingreheated by the heating elements 20, 2I while only a small fractionescapes through the slots 2, 3 to effect the aforesaid equalization, theair present in the chamber I is progressively replaced by superheatedsteam.

Since the only connection between the interior of the chamber I and theatmosphere is by way of the slots 2, 3, and since the continuousvaporization produces a pressure greater than atmospheric pressurewithin the chamber, the equalizing fluid flows are directed from theinterior toward the exterior of the chamber, thereby opposing the entryof fresh air of atmospheric pressure.

Thus, after a certain starting period, the fluid inside the chamber willconsist substantially exclusively of superheated steam having a suitabletemperature ranging, preferably, between and C. and maintained at thislevel by the heating'elements 20 and 2I.

The pressure differential desired to be maintained between the interiorof the chamber I and the atmosphere may be controlled by means of theplates 22, 23 which may be adjusted as to the clearance of the slots 2and 3, i. e. the

cross section of the discharge channels con-.

stituted thereby.

It may be mentioned that it is desirable to reduce the volume of thechamber I to a minimum, in order to decrease the surface of radiationand also the quantity of air which is to be heated.

The method according to the invention offers substantial advantages incomparison with known drying precesses. With respect to drying. by hotair, the method according to the invention affords an appreciable savingof heat by eliminating the large heat losses which are due to thenecessary discharge of saturated and hot air into the atmosphere.Furthermore, the process according to the invention permits of a morerapid and uniform drying operation than heretofore known processesoperating with temperatures below 100 C. It is to be stressed that themoisture to be expelled is present not merely on the surface of thefabric but also bound in the very interior or center (core) of theflbers.

While, in conventional drying processes, the surface moisture isevaporated directly by the blowing hot air, the liquid or water presentin the core of the fibers (bound moisture) must first rise to thesurface by capillary action before being able to evaporate, whichrequires a relatively long time. According to the present invention andin contradistinction to the prior art the use of superheated steam withtemperatures above 100 C. and having sufiicient high velocity whenimpinging on the material results in the partial condensation of saidsuperheated steam, whereby latent heat thereof is liberated which causesincrease of the temperature of the mate:

rial to the boiling point of the liquid or water and thus directvaporization in and elimination of the waterfrom the very heart of thefibers occurs by expansion, so that said liquid escapes in the form ofvapor or steam instead of rising to the surface in liquid state bycapillarity as is the case in said conventional drying precesses.

According to a feature of the invention, the apparatus described ispreferably operated at a speed such that the article to be dried emergesfrom the heating chamber as soon as a sufficiently high degree ofdryness is reached.

It is pointed out that, in a process according to the invention, it isimpossible ever to arrive at a complete dryness even if the articleshould remain in the chamber for a time longer than necessary for theexpulsion of the excessive moisture resulting from the treatment orimpregnating liquid. One of the reasons therefor is that drying may takeplace in an atmosphere represented by the vapor of the permeating orimpregnating liquid. Accordingly, there will never occur so much loss ofmoisture that the article dried will become brittle and unmanageable iyet the resulting degree of dryness is at least equal to, if not greaterthan that generally attainable by drying in the open air. In thisconnection it may be mentioned that the normal moisture content inherentin wool is about 18%, while that of most other fabrics ranges from 3% toabout 16%; these percentages are readily obtainable by the methodaccording to the invention.

Should, therefore, the article be accidentally left in the apparatus fora period longer than normal, no hardening or other harmful effects willresult such as would occur if the drying took place in an atmosphere ofdry and warm air; this is one of the important advantages of theinvention.

Referring, now, to the apparatus shown in Fig. 3, there is provided achamber 3| which is divided by a partition 32 into two compartments Aand B through which passes a web 33 of fabric or any other endlessfibrous material or article to be treated. This web enters the chamber3! through the entrance slot 35;, passes subsequently through slot 35 ofpartition 32 and leaves the apparatus by way of the exit slot 35.

Each of the compartments A, B comprises an upper and a lower blower unit3? and .38, re-

spectively, which are provided at their opposed surfaces with dischargetubes or nozzles 39 and Gil, respectively. Heating elements GI, 42 aredisposed within the units 3?, 38. The discharge nozzles 39, iii aresupplied with circulating fluid by the blowers d3, 44.

The fluid, such as steam, is injected'into the units 31 and 38 by meansof perforated pipes 45 and 56, respectively, which are connected to acommon inlet duct M.

The web 33 to be treated, which is transported toward the inlet slot 3!;by way of suitable guide roller means 4-3, passes over rollers 39 and 5ddisposed, respectively, adiacent the inlet and the outlet of chamber 3i.

Exhaust pipes 5! and 52, which communicate with a common outlet duct 53leading toa regenerator or heat exchanger (not shown), extend into thecompartments A and B, respectively.

The vapors escaping through the inlet and outlet slots 34, 36, owing tothe superatmospheric pressure prevailing in the compartments A and B,are directed to collector pipes 56, 5'5 which likewise communicate withthe duct 53. Each collector is, for this purpose, arranged to dorm atight seal substantially preventing the escape of fluid into theatmosphere while allowing for the movement of the web 33. As shown onthe left-hand side of Fig. 3, the lower end of the collector pipe 55 isprovided with two lips 56, 5'! bearing in a fluid-tight manner upon theroller 49 and an auxiliary roller 58, respectively. A slightly differentconstruction is shown on the right-hand side of Fig. 3 where the lips56a and 51a, provided on the lower end of collector pipe 55, bear uponthe roller 50 and upon the underside of the web 33, respectively.

The heat exchanger connected to the duct 53 may take the form of acondenser serving as a source of hot water, obtained from thecondensation of the vapors from chamber 31 and adapted to feed, forexample, a boiler, and also as a source of heat which is liberated inthe condensation process. The vapor collected by duct 53 may, of course,also be utilized for any other purpose; thus it may, for example, serveto energize a lowpressure turbine or similar machine before beingconducted to a heat exchanger or condenser.

To promote the circulation and the recovery of the vapors, ventilatinmeans 53a similar to the blowers d3, d4 may also be disposed in theoutlet duct 53 and/or in the collectors 5d, 55.

The c aeration of the apparatus shown in Fig. 3 isas follows:

In accordance with a further feature of the invention, the air initiallypresent in the compartments A, B is removed from the chamber 3i beforethe drying process proper gets under way, in order to insure that thearticle to be dried be treated in substantially air-free atmosphere fromthe very beginning; in this manner the drying of the entire web or otherarticle tai-zes place under essentially uniform conditions. To this end,the compartments A and B are first heated by means of the heatingelements all and t2. 'As soon as the desiredtemperature is reachedseturated steam (or atomized hot water admitted through the perforatedpipes 53 by way of the common inlet duct il provided, for this purpose,with a valve 59, shown. The saturated vapor thus admitted (or producedby vaporization of the introduced water as the result of the hightemperature obtaining the chamber 3 i) is now circulated ide t partmentsA B by means of the blows I in such manner to drive the air out of thechamber This notion is assisted by rise in pressure, pr iuced by theintroduction of the vapor and may be further accelerated by theprovision of additional ventilating means as previously mentioned.

After the air in the chamber Si is srificientiy rarefied or removed, theweb 33 to M dried is introduced into the compartment A in order to bedried the manner described in connection with Figs. 1 and 2, Since theevaporation of the moisture contained in the web 33 produces additionalsteam, the 'ection of vapor by way of the pipes Q5 and 4t be stopped orat least throttled to such an extent that the added vapor, together hthe vapor produced inside the chamber, just i .eintain the desiredoperatin conditions, that is so say, to maintain a slight gauge pressureis]. preventing the re-entrance of any air.

As above described, the heat required to maintain the temperature in thecompartments A, Bis produced by heating elements ii, It is, however,also possible to obtain the necessary heat dur the operation of theapparatus by admitting, through the duct ii, steam of such temperature,pressure and degree of saturation that, upon a sudden expansion of thatsteam in entering the compartments A and B, a transformation intosuperheated steam of suitable temperature takes place. In such case, itwill be possible to entirely dispense with the heating elements 43 and44, or at least to reduce their capacity. Assuming, by way of example,that saturated steam under a pressure of kg./cm. is admitted into thechamber, one obtains, upon a sudden expansion, superheated steam of acalculated temperature of 150 C. in the compartments A and B. Thissuperheated steam, when discharged with high velocity through thenozzles 39, 40 by means of the blowers 43, 44 so as to repeatedlyimpinge upon the web 33, effects through partial condensation uponcontact with the web material (liberated latent heat) the vaporizationof a large portion of the permeating liquid in the web material.

The use of superheated vapor, in the manner just stated, should becontrolled in dependence upon the temperature of the vapor, on the onehand, and its speed of circulation over and across the article to bedried, on the other hand.

Each article has a critical temperature above which the article maysuifer damage, yet this temperature may be exceeded for a certaincritical timewithout harmful elfects to the article. It is, therefore,necessary to produce. the desired effect (1. e., to obtain the desireddegree of dryness) within a period not greater than this critical time;the temperature may then be safely raised above the critical limitreferred to.

To this end, it is necessary to circulate the drying fluid or vapor, ata speed such that the operation will be completed within a time lessthan the critical time. Let us assume, for example, that the criticaltemperature of an article is 150 C. and that, at this temperature, thecritical time is five (5) minutes. It will then be necessary to completethe operation in less than five minutes if the operating temperature isof the order of 150 0., better results being obtainable with shorteroperating periods so that a two-minute treatment is to be preferred overa threeminute treatment.

The desired shortness of the treatment may, in all instances, beobtained by suitably conditioning, for example, by increasing thevelocity of the circulating treatment vapor (superheated steam). Thisvelocity, in turn, may be held to reasonable values by arranging thelayout of the apparatus so that the treatment vapor may impinge readilyupon the surface of the article, whereby the projected vapor moleculesdo not meet any obstacles, thus avoiding the formation of a static layeror stratum of fluid adjacent the article to be treated. It will also beevident that the nozzles are to be designed for maximum efllciency, byproviding them with a sufiiciently large cross section and reducing thenumber of elbows and other obstacles to a minimum.

A construction of such nozzles is more explicitly described in mycopending application Serial No. 756,876, filed June 25, 1947.

In view of fresh vapor supply by means of pipes 45 and 45 and due tocontinuous evaporation which takes place in chambers A and B thequantity of vapor existing in these chambers is constantly increased andmust be removed in order to maintain a constant superatmosphericpressure within the apparatus. This withdrawal of vapor is effectuatedby means of collectors 5i and 52. Besides, this, vapor escapes in'aspontaneous manner under the influence of the prevailing overpressure(superatmospheric pressure) through the slots at the inlet and outlet 34and 36 and is captured and conducted into exhaust pipes 54 and 55.

It is further possible, in the plant shown in Fig. 3, to introduce thevapor through the conduit 41 and let said vapor pass first through theheating elements 6!, 42 before conducting the same through perforatedpipes 45, 46, the vapor thus serving, indirectly, as a heating meansbefore serving as a drying means.

It will be understood that the vapors collected in the outlet duct 53need not be utilized in any external device but may be returned to thesystem, to be reinjected (after reheating and/or recompression, ifnecessary) by way of the inlet duct 41. While, in the precedingdescription, the permeating liquid has been assumed to be water, theinvention is equally applicable to the expulsion of other liquids fromarticles of various descriptions.

Thus, the invention will be seen to provide a method of drying anarticle permeated by a liquid which comprises exposing said article to agaseous fluid having a temperature higher than the boiling point of saidliquid, preferably the vapor oi the liquid itself, and substantiallyexcluding air from contact with the article during such exposure.

According to another of its aspects, the invention will be seen toprovide a drying apparatus comprising a chamber I, 35 provided with oneor more openings 2, 3, t l, 36 for the insertion and/or withdrawal ofthe article, and heating means 20, 2|, 4|, 32, 45, 46 inside saidchamber adapted to raise the temperature therein above the boiling pointof said liquid, whereby part of said liquid will change into vapor,thereby raising the pressure inside said chamber, said opening oropenings having a size such as to enable said pressure substantially toprevent the entrance of fresh air into said chamber.

It will thus be seen that there has been provided according to theinvention a method of treating or drying fibrous sheet material whichcontains an impregnating liquid and which is adapted to be moved througha substantially airfree heating enclosure; comprising the steps ofimpinging on spaced surface areas of said material jets of superheatedsteam conditioned with respect to its velocity to partly condense saidsuperheated steam and to liberate enough latent heat therefrom on.saidmaterial to thereby raise the temperature of the material to the boilingpoint of said liquid and to transform bound moisture within the materialto vapor, which is forced by expansion within said material to thesurface thereof, creating suction between said spaced surface areas tothereby draw off said vapor from said surface of said material, andreheating said vapor to arrive at the condition of said superheatedsteam.

It will further be understood that the invention is capable of numerousadaptations and modifications, particularly in regard to theconstructive details shown; for example, the adjusting means 22, 23 maybe modified, or supplemented by additional adjusting means, so as to notenable only the width but also the length of the slots 3, 4 to bevaried. Other changes will undoubtedly occur to those skilled in the artand are intended to be included in the scope of the invention as definedin the objects and in the appended claim.

Having thus described the invention what is claimed as new and desiredto secure by Letters Patent, is:

The method of treating fibrous sheet material which contains animpregnating liquid and which is adapted to be moved through asubstantially air-free heating enclosure; comprising the steps ofimpinging on spaced surface areas of said material jets of superheatedsteam conditioned :ith respect to its velocity to partly condense saidsuperheated steam and to liberate enough latent heat therefrom on saidmaterial to thereby raise the temperature of the material to the boilingpoint of said liquid and to transform bound moisture within the materialto vapor, which is forced by expansion within said material to thesurface thereof, creating suction between 10 said spaced surface areasto thereby draw oii said vapor from said surface of said material, andreheating said vapor to arrive at the condition of said superheatedsteam.

JULIEN DUN'GLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,228,225 Lynah May 29. 19172,008,230 Spooner July 16, 1935 2,119,261 Andrews May 31, 1938 2,189,915Mellor et a1 Feb. 13, 1940 2,225,505 OiTen Dec. 17, 1940

